The Memotech MTX500, MTX512 and RS128 were a series of Zilog Z80A processor-based home computers released by Memotech in 1983 and 1984. They were technically similar to MSX computers, but were not compatible.

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The MTX500 had 32 KB of RAM, the MTX512 had 64KB, and the RS128 had 128KB. Although the Z80A could only address a maximum of 64KB at a time, the MTX and RS128's extra memory, up to a maximum of 768KB, was accessible through the technique of page switching. All models had 32KB of ROM accessible in the first 24KB of address space. The extra 8KB of ROM was available through page switching. The ROM could be switched out entirely, allowing the full 16-bit address space to be used for RAM.

The computers featured an all-aluminium case and full size keyboard with real keys (unlike the chiclet keyboard used on the Sinclair ZX Spectrum). In addition to the standard (for the time) BASIC language interpreter, it included some other software:

The computers also featured support for plug-in ROM cartridges (a little like the BBC Micro). The most popular of these was the ISO Pascal language from HiSoft which was much faster than interpreted BASIC. A considerable addition to any Memotech system was the hugely expensive FDX system which added 5.25" floppy disk drives, Winchester hard disks and CP/M 2.2 operating system. A Memotech badged CGA monitor was also made available around the time of the FDX launch.

The Norwegian company Norbit Elektronikk Norge A/S run by Anne Selene Fiko developed a complete Input/Output (I/O) control system, with 4× 16-bit (by swapping 8 bits at time) I/O ports, 8-bit Analog-to-digital converter and 8-bit Digital-to-analog converter, all with sensor systems for robotics and controls. The control system was designed for the same aluminium casing as the main MTX512 unit. At that time Memotech were working on a huge project to deliver Memotech MTX512 together with the FDX and the control unit from Norbit Elektronikk to 64,000 schools in the USSR. The USSR was at that time also under embargo by the United States so companies were not allowed to deliver the new IBM Personal Computers with MS-DOS, but CP/M computers were not included in the Soviet embargo blockage.

Memotech went into receivership in 1985. A contributing factor, beyond the poor commercial success of the MTX, was the substantial investment Memotech made in preparing the MTX for the Soviet deal. This required a red brushed aluminium case instead of black, Russian BASIC, a Russian keyboard and Russian documentation. Memotech worked with Oxford University on the internationalisation. Memotech did not receive funding they expected from the British government for this project.

The Soviet government was also evaluating computer systems from other manufacturers. Memotech required cash payments prior to supplying 64,000 computers. The Soviets decided against this cash deal and instead agreed to acquire MSX computers from Yamaha (another later big deal was with Daewoo) with payment mainly in steel and oil. About 64,000 MSX computers had been supplied to USSR schools and other educational institutions.[citation needed]

Since Memotech lost the deal to the Soviet Union, and they had invested all their money, borrowed money from the banks, plus got about £1m funding from the UK government, Memotech went bankrupt. Some of the Memotech inventions still lived on, as several employees took some of Memotech's new video editing systems for televisions back to the USA, where they are believed[citation needed] to have ended up at Silicon Graphics. As a result of Memotech's bankruptcy, the UK government stopped funding to all computer manufacturers in UK at that time, including Sinclair, Acorn and Apricot.

Control systems from Norbit Elektronikk are still sold under the brand name of MISOLIMA.